From Google images, the Hepco & Becker centre stand uses the same rubber bungs, maybe the fixing bolts and washers are the same? But they only have a spring on the right side not both like the Yammy one.
Other than that you could try breakers yards. I don't know if Partfinder is still in exsistance over there. You register what your after online (or phone when I did it) then it searches hundreds of breakers, then if ones got what your after the breaker will get in touch with you.
Good luck.